Sensorineural deafness is studied through two activities. One activity is the maintainance of an ongoing research clinic (The Special Test Unit) which conducts extensive and innovative audiological examinations of patients with unusual sensorineural losses referred by various otological and audiological sources. From time to time new audiological tests are devised and studied to ascertain their usefulness as diagnostic tools. The other activity involves systematically investigating selected categories of sensorineural loss via otolaryngological, audiological, radiological and other types of analysis. Here the emphasis is on gathering in-depth information of various kinds which can then be subjected to search for relationships that will 1) suggest etiological sub-categories and 2) clarify relations between abnormalities of auditory behavior and the geographic sites, configurations and natures of various lesions and pathologies. A major focus of both activities is on sensorineural involvements whose etiologies are not readily apparent. In this regard, attention will be given to the distinctions between the symptomatologies of peripheral versus central lesions. Early work of this project centered upon cochlear otosclerosis but this work is nearing completion. Emphasis is shifting to other categories.